Avalanche Advisory for Thursday 1-31-2013

Expires midnight 1-31-2013

Tuckerman and Huntington Ravines have HIGH avalanche danger.  Natural avalanches are likely and human triggered avalanches are very likely.  Travel in avalanche terrain is not recommended.

Ever feel like a yo-yo?  If you have felt that up and down sensation viciously repeating itself then you know how the mountain feels right now.  Last week -35F; yesterday and this morning 40’s and raining, and guess what….-15F  tomorrow!!  It’s kind of like an amusement park ride without the amusing part.  Rain, heavy at times, and fog are dominating the mountain this morning.  This coupled with the very high temperatures over the past 24 hours, pushing 50F at some elevations, are the bulls-eye avalanche data points driving the High danger rating today.  Melting around the clock and intense rain are weakening slabs rapidly.  Freewater has eroded bonds within previously cohesive slabs and is working its way down to weak layers of buried faceted crystals that developed during last week’s cold snap.  In addition to wet slab failure, we are also concerned about slush-water-snow blowouts in both Ravines.  When running water behind the snow and ice grows in mass to the point that subterranean channels can no longer handle the force and weight, hydraulic blowouts, which can be catastrophic, send an ugly slush debris flow downhill.  The main concerns for this hazard are near the Lip in Tuckerman and the narrowest gullies in Huntington such as Pinnacle and the junction of Diagonal and Yale.

Currently, it is raining hard and should continue to rain through the morning hours before the front rages through the mountains which will scale back moisture, increase winds, and send temperatures in a tumbling freefall.  Winds will increase blasting over 100mph in alpine zones and gusting to half that amount in the valleys.  Temperatures will drop like a rock, perhaps by 40F degrees by this evening.  This will do a couple of things.  It will begin locking up the existing wet snowpack from the surface down increasing its strength and stability and it will change rain back to snow producing up to 6” (15cm) by later tomorrow.  The transition from one weather scenario, 43F and pouring, to -15F and snowing, will make for some complex avalanche analysis.  As rain/freewater drain and freezing temperatures begin locking up the wet snowpack and increasing stability, new snow loading will be generate other problems.  Ultimately we will be decreasing one avalanche stability problem while increasing the other.  As new snow loads into strong lee pockets it may initially have poor or good adhesion depending on whether the first shot of snow falls on wet surfaces or frozen slick ones.  Either way, as snow builds up and insulates the old warmer snowpack you will likely see some decent bonding.  However, as pockets deepen this will become moot as fracture and new slab failure will likely occur within new snow above the interface with the old surface.

So… the main points for your safety.  1. We will have High avalanche danger this morning before decreasing somewhat this afternoon.  Be prepared for new avalanche concerns as snow loads in with the frontal passage later today and through the evening.  2. Expect VERY slick and hard conditions later today and through the weekend.  Expect to reach Mach1 in the event of a fall, with self-arresting to be unlikely.  Forecasted high winds may blow you off balance.  Crampons, ice ax and the experience to use them will be essential for safe travel.  3. As refreezing occurs, we will have a strong potential for ice damming on many climbs.  These dams of ice holding back running water can build up tremendous hydraulic pressure that can release with a tool placement or crampon penetration.  These are most common near bulges and have caused a number of accidents over the years.  4.  Backcountry skiing and riding will be extremely challenging.  Expect poor, icy, bumpy, core chattering, difficult conditions on the Sherburne ski trail this afternoon.  

 Please Remember:

  • Safe travel in avalanche terrain requires training and experience. This advisory is just one tool to help you make your own decisions in avalanche terrain. You control your own risk by choosing where, when, and how you travel.
  • Anticipate a changing avalanche danger when actual weather differs from the higher summits forecast.
  • For more information contact the Forest Service Snow Rangers, the AMC at the Pinkham Notch Visitor Center, or the caretakers at Hermit Lake Shelters or the Harvard Cabin.Posted 8:30a.m. 1-31-2013 A new advisory will be issued tomorrow.

Christopher Joosen, Snow Ranger
USDA Forest Service
White Mountain National Forest
(603) 466-2713 TTY (603) 466-2856

2013-01-31 Print Version